The invention relates to a method and a device for the treatment of molds to produce an ophthalmic molding, especially an ophthalmic lens, particularly a contact lens.
Contact lenses can be manufactured economically in large numbers by the so-called mold or full/mold process. In this process, the lenses are manufactured into their final shape between two mold halves, with no need to subsequently finish the surfaces of the lenses, or finish the edges. Mold processes are described for example in PCT patent application No. WO/87/04390 or in EP-A 0 367 513.
The contact lenses produced in this manner are molded parts having little mechanical stability and a water content of more than 60% in weight. After manufacture, the lens is inspected, then packed and subjected to heat sterilization in an autoclave.
The geometry of the contact lenses is defined by the mold cavity. The edge of the contact lens is formed by the mold, which normally consists of two mold halves. The geometry of the edge is defined by the contour of the two mold halves in the area where they make contact.
To manufacture a contact lens, a predetermined amount of a flowable starting material is placed in the female mold half. Afterwards, the mold is closed by placing the male mold half thereon. Normally, a surplus of starting material is used, so that, when the mold is closed, the excess amount is expelled out into an overflow area adjacent to the mold cavity. The subsequent polymerization or crosslinking of the starting material takes place by radiation with UV light, or by heat action, or by another non-thermal method.
In U.S. Pat. No. 5,508,317, a new contact lens material is described, which represents an important improvement in the chemistry of polymerizable starting material for the manufacture of contact lenses. The patent discloses a water-soluble composition of a prepolymer, which is filled into the mold cavity and then crosslinked photochemically. Since the prepolymer has several crosslinkable groups, the crosslinking is notable for its high quality, so that a finished lens of optical quality can be produced within a few seconds, without the necessity for subsequent extraction or finishing steps. Owing to the improved chemistry of the starting material as illustrated in the patent, contact lenses can be produced at considerably lower cost, so that in this way it is possible to produce disposable lenses that are used only once.
EP-A-0 637 490 describes a process by means of which a further improvement may be obtained in the preparation process of contact lenses with the prepolymer described in U.S. Pat. No. 5,508,317. Here, the material is filled into a mold comprising two halves, whereby the two mold halves do not touch, but a thin circular gap is located between them. The gap is linked to the mold cavity, so that surplus lens material can flow away into the gap. Instead of the polypropylene molds that may be used only once, reusable quartz/glass molds may be used. Because of the water-soluble basic chemistry, after a lens has been produced, the uncrosslinked prepolymer and other residues can be removed from the molds rapidly and effectively with water, and the molds dried in the air. In this way, high precision of the lens shaping may also be achieved. Crosslinking of the prepolymer takes place by radiation especially with UV light, whereby radiation is restricted to the mold cavity by a chromium screen. In this way, only the material in the mold cavity is crosslinked, so that there is high reproducibility of the edges of the lens without closing the two polypropylene mold halves. The uncrosslinked shaded-off prepolymer solution can be easily washed away from the shaped, crosslinked lens with water.
However, the glass or quartz molds used to make the lenses do not immediately produce lenses without defects. Brand new glass, quartz or fused synthetic quartz molds inhibit crosslinking of the lens polymer. The lens edge is frequently insufficiently polymerized, making the borders of the lens ill defined. A large number of lenses must be made from the new molds before the lenses are of sufficient quality to be sold commercially. The lenses of inferior quality must be discarded. The problems with new molds eventually disappear, however, after a sufficient number of lenses have been made therefrom. This process is referred to as xe2x80x9cburning in xe2x80x9d new molds, and is expensive and time consuming. It is an object of the present invention to pre treat the molds to avoid the burn in procedure.
Therefore, it is necessary to produce a lot of moldings before starting with the production of moldings with the requested quality. However, this is very expensive and time-consuming.
The invention is concerned with the problem of improving the readiness for use of glass, quartz or fused synthetic quartz molds in order to start earlier with the production of moldings having a constant quality.
By coupling UV light into the mold cavity and by irradiating the molds the chemical structure of the glass/quartz surface is changed so that adhesion and deformation of the lens material to the surface can be reduced. This has the effect that high quality contact lenses can be produced considerably earlier, enabling a rapid use of the molds.